How do I calculate the correct length of fastener?

It is important to select a fastener of the correct length for the application. If the fastener is too long, it will take longer to install and will protrude excessively through the substrate. This could cause injury or snag on other construction elements. If the fastener is too short, it will not penetrate the substrate or achieve sufficient embedment. This could cause the fastener to fail because it will not achieve the correct performance values.

To calculate the correct length of fastener, you will need to know the dimensions of the build-up and the substrate:

• Build-up depth

  The build-up refers to the total thickness of everything a fastener is being used to fix. It is measured from the top of the substrate (e.g. the purlin, rail, or deck) to the top of the material being fixed (e.g. roof sheet or panel outer skin). This should include all components in a multi-layer application.

• Substrate depth

  The thickness of the substrate being fixed in to.

Fastener manufacturers provide data on the build-up and substrate thickness that their fasteners are suitable for.

• The maximum and minimum depth of build-up combination a fastener is designed to attach.

• The maximum and minimum substrate thickness a fastener is designed to fix into.

The fastener length should fall comfortably within the maximum and minimum values declared for the depth of substrate, and combined depth of build-up and washer / component.

If more than one fastener is suitable, you should always use the shortest possible fastener for the build-up and substrate depth to ensure that the fastener does not protrude excessively at the back of the substrate.

* The guidelines described are for using Fixfast’s fasteners from the DrillFast and MatchFast range.